Acoustical velocity well logging system featuring simplified exploring unit



Feb. 6, 1968 R. P. MAZZAGATTI ETAL 3 ACOUSTICAL VELOCITY WELL LOGGINGSYSTEM FEATURING SIMPLIFIED EXPLORING UNIT 4 Sheets-Sheet 1 Filed Aprill2, 1966 210 VOLTS [DUO-"- 3,368,196 RING Feb. 6, 1968 R. P. MAZZAGATTIETAL ACOUSTICAL VELOCITY WELL LOGGING SYSTEM FEATU SIMPLIFIED EXPLORINGUNIT Filed April 12, 1966 4 Sheets-Sheet 2 1968 R. P. MAZZAGATTI ETAL3,368,196

ACOUSTIC/AL VELOCITY WELL LOGGING SYSTEM FEATURING SIMPLIFIED EXPLORINGUNIT Filed April 12, 1966 4 Sheets-Sheet 3 s 7. WV\\\VV Z M ,J'y/r c079/70 Genera/or Feb. 6, 1968 R. P. MAZZAGATTI E TAL 3,368,196

VELOCITY WELL LOGGING SYSTEM FEATURING SIMPLIFIED EXPLORING UNITACOUSTICAL Filed April 12, 1966 4 Sheets-Sheet 4 United States Patent3,368,196 ACOUSTICAL VELOCITY WELL LOGGING SYS- TEM FEATURING SIMPLIFIEDEXPLORING UNIT Roy P. Mazzagatti, Bellaire, and Donald J. Dowling andCloy N. Causey, Houston, Tex., assignors to Texaco Inc., New York, N.Y.,a corporation of Delaware Continuation-impart of application Ser. No.842,922, Sept. 28, 1959. This application Apr. 12, 1966, Ser. No.552,996

17 Claims. (Cl. 340-18) ABSTRACT OF THE DISCLOSURE The present inventionrelates to an acoustical velocity well logging system having arelatively simple exploring unit or logging tool adapted to be passedthrough a well bore and which includes an acoustical transmittingtransducer for transmitting an acoustic pulse through earth formationsadjacent the logging tool and which further comprises an acoustic pulsegenerating circuit including an acoustical transmitter transducercomprising a transformer and energy storing means and a siliconcontrolled rectifier, wherein trigger pulse means are disposed at theearths surface adjacent the bore hole and where means are provided forapplying the output of a trigger pulse producing means to the controlelement of said silicon controlled rectifier for periodicallydischarging the energy in said storing means to said transformer toactivate the transmitting transducer and wherein means are furtherprovided for detecting acoustic pulses transmitted through earthformations from said transmitting transducer comprising first and secondacoustic pulse receiving transducers spaced from one another and fromthe transmitting transducer and wherein a transformer means is providedfor coupling the signals detected by the receiving transducers to asignal transmission system for transmitting same to the surface wheretime interval measuring means are coupled to the other end of saidtransmission system for providing an indication of the time intervalbetween the occurrence of given acoustic pulses detected by said firstand second acoustic pulse receiving transducers.

This application is a continuation-in-part of application Ser. No.842,922, filed Sept. 28, 1959, and now abandoned.

This invention relates to an acoustical velocity well logging system andmore particularly to a well logging system having a relatively simpleand inexpensive exploring unit or tool which provides accurateacoustical velocity measurements of formations traversed by a well bore.

In the field of acoustical velocity logging, prior art ;systems utilizea sonde or exploring unit which contains an electroacousticaltransmitting transducer and one or more electroacoustical receivingtransducers. Furthermore, the exploring unit contains an electronictransmitting circuit which provides a sharp pulse to actuate thetransmitting transducer and a receiver amplifier coupled to the outputof each of the receiver transducers. Because of the extensive electroniccircuitry including a substantial number of electronic tube-type devicescontained in the exploring unit, the exploring unit is both large insize and expensive to fabricate or construct.

In field operations it is desirable to have an exploring unit which isof a small size and a rugged construction because of the resulting easeof handling with limited available personnel. It is also, of course,very desirable for economic reasons that the cost of the exploring unitbe reduced from the cost of presently used exploring units. In loggingopen boreholes and seismic shot holes, in particular, the exploring unitof the well logging system is often stuck and eventually lost in theborehole. Accordingly, the exploring unit of the system should be of aninexpensive nature such that a loss of an exploring unit would beeconomically reasonable and such that the use of such an exploring unitwould be considered reasonable for boreholes even in poor condition. Incertain areas seismic shot holes are difficult to drill and afterdrilling the holes may cave in in just a few minutes. In such areasthere is considerable risk of losing an exploring unit and, therefore,with the present relatively expensive units the velocity informationoften is not obtained due to failure to risk losing the unit during therunning of a log of the borehole.

In accordance with the present invention an improved acoustical velocitywell logging system is provided wherein the exploring unit is reduced]substantially in size and complexit as compared to the exploring unitsused in prior art acoustic velocity logging systems. Moreparticularly,the present invention provides an improved acoustical velocity welllogging system which includes an exploring unit which does not contain asingle electronic tube-type device but wherein only a single, or at themost a few, semi-conductor devices need be provided.

For a better understanding of the invention reference may be had to theaccompanying drawing in which:

FIG. 1 illustrates a vertical section through a borehole which containsan exploring unit shown partly broken away to show elements therein,including a schematic representation of the electrical circuitrycontained therein in accordance with the present invention,

FIG. 2 is an enlarged cross-sectional view of the logging cable through2-2 of FIG. 1 which is connected to the exploring unit,

FIG. 3 is a circuit diagram primarly :in block form of the surfaceequipment of the acoustical system of the present invention icluding asectional view of a portion of the earths surface with parts of theapparatus disposed in a borehole therein,

FIG. 4 is a circuit diagram of an embodiment of an acoustic pulsegenerator which may be substituted for the acoustic pulse generator inthe exploring unit illustrated in FIG. 1 of the drawing,

FIG. 5 is an illustration similar to FIG. 1 but showing the down holeexploring unit and circuitry of another embodiment of the loggingsystem.

FIG. 6 is an enlarged cross-sectional view taken through the lines 6-6of FIG. 5, and

FIG. 7 is an illustration similar to FIG. 3 showing the surfaceequipment of the embodiment of FIGS. 5 and 6.

Referring in more detail to the figures of the drawing, a borehole 10containing a borehole liquid, such as conventionally used boreholedrilling mud, is shown traversing a plurality of sub-surface formations12, 14 and 16, the acoustic velocity in which it is desired todetermine. Disposed within the borehole is an exploring unit, sonde orelongated tool 18 supported therein by a multi-conductor cable 20. Theexploring unit 18 is made up of a plurality of sections which include,from top to bottom, a packing gland 22, a transmitter circuit housing24, a first spacer 26, a transmitting transducer 28 which includes afirst electrostrictive acoustic element 29, preferably a lead zirconatetitanate ceramic cylinder which may have 1.5" length x 1.5 diameter x/s" wall thickness dimensions, a second spacer 30, a first receivingtransducer 32 spaced, preferably, one foot from the transmittingtransducer 28 and which includes a second electrostictive acousticelement 33, preferably, a barium titanate ceramic cylinder, a thirdspacer 34, a second receiving transducer 36, spaced, preferably, onefoot from the first receiving transducer 32 and which includes a thirdelectrostrictive acuostic element 37, preferably, also a barium titanateceramic cylinder, a fourth spacer 38, a receiver transducer transformercompartment 40 and a boot 42. The spacers 26, 30, 34 and 38 arepreferably made of Teflon.

The multiconductor cable provides means for coupling electrical powerand signals between the surface equipment and exploring unit of theacoustical system according to the present invention. These signalsinclude appropriate synchronizing signals, hereinafter referred to assy-nc signals in accordance with common usage in this art. Inparticular, the cable 20 has first and second coaxial cables 44 and 46,a common ground conductor 48, a sync signal conductor 50, an electricalpower conductor 52, a cable spacer 53 and a stainless steel center cable54, as shown in FIG. 2, and an outer jacket 56. The coaxial cables 44and 46 are, preferably, miniature coaxial cables such as the AmphenolSubminax coaxial cable No. 21- 598 and the stainless steel center cable54 must be of sufficient strength to support the exploring unit 18 aswell as the weight of the cable 20 in the borehole.

An acoustic pulse generator circuit 58, includes a semiconductor device60 which is a three-terminal solid-state thyratron of the type describedin an article entitled Solid-State Thyratrons Available Today in theMar. 6, 1959 issue of Electronics on pages 50 and 51, and prefer ably asilicon controlled rectifier.

The silicon controlled rectifier 60 is, preferably, a General Electricsilicon controlled rectifier type Z] 39A- 250 or type C35H which arePNPN high-power bistable controlled switching devices. The anode of thesilicon controlled rectifier 60 is connected to the electrical powerconductor 52 through an anode resistor 62. The control element of thesilicon controlled rectifier 60 is connected to the sync signalconductor 50 through a coupling capacitor 64. The control element of thesilicon controlled rectifier 60 is connected also to ground through acontrol element resistor 66. The cathode of the silicon controlledrectifier 60 is connected directly to ground. The anode of the siliconcontrolled rectifier 60 is connected also to one terminal of the primarywinding 68 of a step-up transformer 70 through a pulse forming networkwhich is, preferably, a capacitor 72, the other terminal of the primarywinding 68 being connected to ground. The secondary Winding 74 of thestep-up transformer 70 is connected directly across the lead zirconatetitanate electrostrictive element 29 and a silicon diode 76 may beconnected directly across the secondary winding 74 to serve as dampingmeans for the acoustic pulse generator circuit 58. Very satisfactoryresults have been obtained when the primary winding 68 of the step-uptransformer 70 had turns and the secondary winding 74 and 250 turns.

The first receiving transducer 32 and, more particularly, the firstbarium titanate electrostrictive element 33, is connected across theprimary winding 78 of a second transformer 80. The secondary winding 82of the second transformer 80 is connected to the first coaxial cable 44.The second receiving transducer 36 and, more particularly, the secondbarium titanate electrostrictive element 37, is connected across theprimary winding 84 of a third transformer 86 which has its secondarywinding 88 connected to the second coaxial cable 46.

At the earths surface the cable 20 passes over a cable measuring device90. The sync signal conductor 50 and the common ground conductor 48 ofthe cable 20 are connected to a sync signal generator 92. The syncsignal generator 92 may be of a conventional type which produces pulsesat a constant repetition rate. A power supply 94 is connected to theelectrical power conductor 52 of the cable 20 and it is also connectedto the common ground conductor 48. The power supply 94 may be of aconventional design for producing required voltages for the electronicdevices in the borehole and in the surface equipment. Since the powersupply 94 may be of the conventional type details thereof are notillustrated in the drawings. The sync signal generator 92 is connectedalso to a sync signal delay circuit 96. The sync signal delay circuit 96may be a one shot multivibrator followed by a ditferentiator. The outputfrom the sync signal delay circuit 96 is applied to a first channel gate98.

The first coaxial cable 44 is connected to a first channel amplifier andtrigger circuit 100, the output of which is connected to an elapsed timemeasuring circuit 102. The first channel gate 98 is connected to thefirst channel amplifier and trigger circuit 100 so as to render thefirst channel amplifier and trigger circuit 100 operative during onlyperiods of time in which a signal from the first coaxial cable 44 isexpected to be applied thereto. The output from the first channelamplifier and trigger circuit 100 is also applied to a delay unit 104which may be somewhat similar to the sync signal delay circuit 96. Asecond channel gate 106 is connected to the output of the delay unit104.

The input of a second channel amplifier and trigger circuit 108 isconnected to the upper end of the second coaxial cable 46 and the outputof the second channel amplifier and trigger circuit 108 is connectedalso to be elapsed time measuring circuit 102. The second channel gate106 is connected to the second channel amplifier and trigger circuit 108so as to render the second channel amplifier and trigger circuit 108operative during only periods of time in which a signal from the secondcoaxial cable 46 is expected to be applied thereto.

The elapsed time measuring circuit 102 may include a bistablemultivibrator responsive to the pulses from the first and second channelamplifier and trigger circuits 100 and 108, a sawtooth generator whichis responsive to a voltage wave from the bistable multivibrator and apeakreading vacuum tube voltmeter, as described in more detail in US.Patent 2,931,455, granted Apr. 15, 1960, on

the basis of the copending US. patent application of R. J;

Loofbourrow having Ser. No. 574,844, filed Mar. 29, 1956, which is acontinuation application of US. application having Ser. No. 157,495, nowabandoned. The output from the elapsed time measuring circuit 102 isapplied to a conventional recorder 110 through a direct current rvoltage amplifier 112. The speed or rate of travel of the tape or chartin the recorder 110 is controlled by the cable measuring device 90,which is connected thereto by coupling means 114.

As illustrated in FIG. 3, the surface equipment may include acalibrating circuit 116 which can be made selectively responsive to theoutput voltage from the sync signal delay circuit 96. The calibratingcircuit 116 produces an output signal which is first applied to at leasta late stage of the first channel amplifier and trigger circuit 100 andat a known later time to at least a late stage of the second channelamplifier and trigger circuit 108. The calibrating circuit 116 may alsohave an output connected to the first and second channel gates 98 and106 to render the first and second channel gates 98 and 106 inoperative,that is, insensitive to the pulses from the first and second coaxialcables, while the calibrating circuit 116 is supplying pulses to thefirst and second channel amplifier and trigger circuits 100 and 108 tocalibrate the elapsed time measuring circuit 102 and the recorder 110.

In operation a pulse of, for example, volts and four microsecondsduration, from the sync signal generator 92, is applied to the syncsignal conductor 5t] of the cable 20 and through the coupling capacitor64 to the control element of the silicon controlled rectifier of theacoustic pulse generator circuit 58 so as to effectively connect thestorage capacitor 72 across the primary winding 63 of the transformer79. When the capacitor 72 is connected across the primary winding 68 theenergy in the capacitor 72 is discharged through the primary winding 68to produce therein an approximately 100 ampere current surge andthereacross a voltage of the order of volts, and a voltage t of theorder of +1750 volts and of 13 microseconds duration across thesecondary winding 74 of the transformer The silicon diode 76 isconnected across the secondary winding 74 so as to effectively groundthe negative voltages developed across the secondary winding 74. Thepositive voltage t across the secondary winding 74 is applied to thelead zirconate titanate electrostrictive element 29 to produce anacoustic pulse T which passes through the borehole fluids surroundingthe exploring unit 18 to the subsurface formations, such as 12, 14 and16. The positive voltage t produces, more accurately, a train ofacoustic pulses rather than a single acoustic pulse, however, sincemeasurements are made between the first pulse of each train, referencewill be made to an acoustic pulse rather than to a train of pulses. Thetransmitted acoustic energy from the transmitting transducer 28 of thesystem of the present invention is increased several times that producedby known well logging acoustic pulse generators utilizing a comparableamount of electrical energy. Furthermore, the acoustic generator of thesystem of the present invention does not require the use of a highvoltage power supply to provide the desired acoustic energy.

A portion of the acoustic energy from the electrostrictive element 29entering into the subsurface formation is refracted and passes throughthe formations toward the receiving transducers 32 and 36. A portion Tof the refracted energy enters into the borehole fluid to strike thefirst barium titanate electrostrictive element 33 to produce across theelectrostrictive element 33 an electric pulse or signal whichcorresponds to the acoustic energy received at electrostrictive element33. The electric energy is applied to the first coaxial cable 44 throughthe second transformer 80. At an instant of time after the acousticenergy is received by the first barium titanate electrostrictive element33, another portion T of the refracted acoustic energy is received atthe second barium titanate electrostrictive element 37 to producethereacross an electric pulse or signal t corresponding to the acousticenergy received at the second barium titanate electrostrictive element37. This electric pulse t is applied to the second coaxial cable 46through the third transformer 86. The second and third transformers 8tand 86 are contained in the receiver transducer transformer compartment40 which is located a considerable distance from the acoustic pulsegenerator circuit 58 so as to minimize the possibility of inducing avoltage in the windings of these transformers and 86 by the energy inthe acoustic pulse generator circuit 58.

The pulse from the sync signal generator 92, which was applied to thecontrol element of the silicon controlled rectifier 69, is applied alsoto the sync signal delay circuit 96. The sync signal delay circuit 96produces a pulse at its output which is delayed by an interval of timewhich is less than the expected shortest interval of time of travel ofan acoustic pulse between the transmitting transducer 28 and the firstreceiving transducer 32. The first channel gate 98, which is responsiveto the pulse produced at the output of the sync signal delay circuit 96,produces at its output a voltage wave or pulse having a time durationwhich is not less than the time diiference between the expected shortesttime of travel of an acoustic pulse from the transmitting transducer 28to the first receiving transducer 32 and the expected longest time oftravel of an acoustic pulse from the transmitting transducer 28 to thefirst receiving transducer 32 through the subsurface formation locatedbetween these two transducers. The pulse from the first channel gate 98is applied to the first channel amplifier and trigger circuit 100 torender this circuit 190 operative only during that time duration.Accordingly, during that time duration the pulse I from the firstreceiving transducer 32, which is being transmitted through the coaxialcable 44, should be received in the first channel amplifier and triggercircuit 100. This pulse I will be applied to the first channel amplifierand trigger circuit 150 to be amplified therein and to produce a sharptrigger pulse at the output thereof which is applied to the elapsed timemeasuring circuit 102 to initiate the measurement of the travel time ofthe acoustic energy through the subsurface formation between the firstand second receiving transducers 32 and 36. The pulse from the output ofthe first channel amplifier .and trigger circuit ltlt) is applied alsoto the delay unit 164 which produces at its output a pulse delayed foran interval of time which is less than the expected shortest interval oftime of travel of the fastest acoustic pulse through the subsurfaceformation between the first receiving transducer 32 and the secondreceiving transducer 36. The pulse from the output of the delay unit 104is applied to the second channel gate 106 so as to initiate a voltagewave or pulse at the output of the second channel gate 106 having a timeduration which is not less than the difference in time between thearrival of the earliest expected acoustic pulse and the last expectedacoustic pulse at the second receiving transducer 36 which passesthrough the subsurface formation between the first and second receivingtransducers 32 and 36. The pulse from the output of the second channelgate 106 is applied to the second channel amplifier and trigger circuit108 to render this circuit 108 operative only during the interval oftime when the pulse from the second channel gate 196 is being appliedthereto. Accordingly, the electrical pulse t from the second bariumtitanate clectrostrictive element 37 which is transmitted through thesecond coaxial cable 46 should arrive at the second channel amplifierand trigger circuit 108 during this interval of time to be amplifiedtherein and to produce a sharp trigger pulse at the output of thiscircuit 108 which is applied to the elapsed time measuring circuit 102to terminate the operation of the elapsed time measuring circuit 102.The output from the elapsed time measuring circuit 102 is then amplifiedby the direct current voltage amplifier 112 and recorded in the recorder110.

When it is desired to calibrate the elapsed time measuring circuit 102and the recorder 11%, the calibrating circuit 116 may be energized toproduce a bias voltage which is applied to the first and second channelgates 98 and to render these gates 98 and 106 inoperative during theperiod of time in which calibrating pulses from the calibrating circuit116 are being transmitted from the output of the calibrating circuit 116to the elapsed time measuring circuit 162. The calibrating circuit 116may include a one shot multivibrator that is actuated by the pulse fromthe sync signal delay circuit 96 to produce a square voltage wave havinga time duration which is equal to the time of travel of an acousticpulse of a given velocity between the first and second receivingtransducers 32 and 36. From this square voltage wave a pair of pulsesmay be obtained, in any known manner, which are separated in time by theduration of the square wave. The first pulse of this pair of pulses isapplied to at least a portion of the first channel amplifier and triggercircuit 100 to produce at the output thereof a trigger pulse which isapplied to the elapsed time measuring circuit 102. The second pulse ofthis pair of pulses is applied to at least a portion of the secondchannel amplifier and trigger circuit 108 to produce a sharp triggerpulse at the output thereof which is applied to the elapsed timemeasuring circuit 162. If desired, the calibrating circuit 116 mayinclude a combination switch which can turn off the channel gates 98 and106 and turn on the calibrating circuit 116.

FIG. 4 illustrates another embodiment of an acoustic pulse generatorwhich may be substituted for and which, in general, is similar to theacoustic pulse generator 58 illustrated in FIG. 1. In this embodiment ofthe generator, the sync signal conductor 50 of the cable 20 is connectedto the control element of a silicon controlled rectifier 60' through aresistor 122 and a first diode 124, having its cathode connected to thecontrol element of the controlled rectifier 60. A second diode 126 isconnected between the control element and the cathode of the silidiode126 being connected to the control element of the controlled rectifier60'. The electrical power conductor 52 of the cable 20 is connected tothe anode of the silicon controlled rectifier 60' through an anoderesistor 12 8. A third diode 130 is connected across the output of thesilicon controlled rectifier 60, the cathode of the third diode 130being connected to the anode of the controlled rectifier 60'. Connected,also across the output of the silicon controlled rectifier 60 is theseries combination of a storage capacitor 132 and a primary winding 134of a step-up transformer 136. A secondary winding 138 of the transformer136 is connected across the transmitting transducer 28. A pair ofserially connected diodes 140 and 142 is connected also across thetransmitting transducer 28, the anode of one diode 140 of the pair ofdiodes being connected directly to ground, or the common groundconductor 48, and the anode of the other diode 142 of the pair of didoesbeing connected to ground through the one diode 140.

In one embodiment of applicants invention as shown in FIG. 4, thesilicon controlled rectifier 60 may be a type C35H, the first diode 124may be a type IN645, the second diode 126 may be a type IN645, the thirddiode 130 may be a type IN1125R and the pair of serially connecteddidoes 140 and 142 may each be a type IN1131. With a B] source of +210volts the anode resistor 128 may have a value of 1,000 ohms. The inputresistor 122 may have a value of 200 ohms. The storage capacitor 132 mayhave a value of 5 microfarads. The primary winding 134 of transformer136 may appropriately have 25 turns and the secondary winding 138 mayhave 250 turns.

Accordingly, it can be seen that an improved acoustical velocity welllogging system has been provided which has in its exploring unit aminimum of electrical com ponents and which does not include a singleelectronic tube.

Of course, it should be understood that the surface equipment mayinclude vacuum tube amplifiers and power supplies but if desired, thecircuitry may include transisters and, accordingly, require less powerand be more portable.

Thus, it can be seen that the acoustical velocity logging system of thepresent invention has provided advantages of improved performance, easeof field operation, more ruggedness due to absence of electronic vacuumtubes, less expense in fabrication costs, and being more readilyaccepted by field personnel because the loss of the exploring unit ofthe present invention, for example, in a seismic shothole, would not bereflected as such an undesirable technical and economic problem as wouldthe loss of presently used exploring units. The cost of constructing theexploring unit of the present invention has been found to be less thanone-fourth of the cost of constructing the most inexpensive exploringunit of any known acoustical velocity well logging system usedheretofore.

Although a system employing an exploring unit having two receivingtransducers has been shown, it should be understood that an exploringunit having only one receiving transducer may be employed, timemeasurements 1 con controlled rectifier 60', thecathodeof these.cond.....

8 being made between pulses t and t by employing switches 118 and 120,as illustrated in FIG. 3 of the drawings, to disconnect each contactpoint a from and to electrically connect each contact point I; to theelapsed time measuring circuit 102.

The further embodiment illustrated in FIGS. 5, 6 and 7 is substantiallyidentical with the embodiments illustrated in FIGS. 1 through 4, withthe exception that the cable 220 of FIGS. 5, 6 and 7 differs somewhatfrom the cable 20 of FIGS. 1, 2 and 3 and with the further exceptionthat the sync signal generator 2 is located in the down hole loggingunit 22 rather than with the surface equipment as shown in FIG. 3 of thepreviously described embodiment. V V V V V In the system of FIGS. 5, 6and 7, the logging cable 220, particularly as shown in detail in FIG. 6,comprises four twisted conductor pairs 244, 246, 250 and 252. Each ofthe conductor pairs consist of two copper conductors twisted about oneanother along the cable, with each conductor of the respective pairsbeing individually provided with a surrounding sleeve of insulatingmaterial such as Teflon having good insulating properties under theconditions of temperature and pressure encountered in bore holes whichmay be 5000 or more feet in depth. Each twisted pair of insulatedconductors is enclosed within an electrical shield advantageouslycomprising a braided copper sheath which, in turn, is enclosed within aninsulating jacket preferably formed of material such as nylon whichserves to insulate the respective shields from one another and from therest of the cable. In addition to the four thus described twisted pairsof conductors the cable 220 is provided with first and second individualconductive wire members 301 and 302 each of which is advantageouslyconstructed of stranded copper wires enclosed within an insulatingmaterial such as polyethylene. The cable 220 further comprises acentrally disposed steel supporting cable stress member 254advantageously in the form of a stainless steel stranded cable ofsufficient strength to support the logging unit 22 and the portion ofthe cable 220 suspended in the bore hole. The stress member 254 iswrapped in adhesive tape which serves to reduce the likelihood ofabrasive damage to the insulation of the surrounding conductors. Thefour twisted conductor pairs each with its respective electrical shieldand nylon jacket are disposed along with the individual conductors 301and 302 in symmetrical relationship in generally tangential matingcontact around the centrally located stress member 254. The cable 220 isfurther provided with a wrapping of fiberglass and an outer fluidtightjacket 256 advantageously formed of rubber-like material of thesynthetic type such as polyvinyl material having the requiredflexibility resistant to bore hole fluids and conditions of temperature,pressure and abrasion. The interstices within the outer cable jacket 256are filled with a suitable cable core filler material in a manner knownin the art.

The twisted conductor pair 244 (conductor pair number 1) couples theoutput of the first receiver 33 in the borehole logging unit to thefirst channel amplifier and trigger circuit 1G0 at the surface.

The twisted conductor pair 246 (conductor pair number 2) couples theoutput of the second receiver unit 37 in the borehole logging unit tothe second channel amplifier and trigger circuit 108 at the surface.

The conductor pair 252 connects the power supply 94 at the surface tothe acoustic transmitter pulsing circuit 58 and sync signal generator92, both of which are located in the downhole logging unit.

The twisted conductor pair 250 (conductor pair number 4) couples theoutput of the sync signal generator 92 in the downhole logging unit tothe sync signal delay circuit 96 at the surface.

It is noted that the sync signal generator 92 in the downhole loggingunit of FIG. 5 is shown provided with a single pair of output leadsconnected to the downhole end of the twisted pair of conductors 250(conductor pair number 4) and to the acoustic transmitter pulsingcircuit '58. In accordance with a further embodiment of the invention(not illustrated) it is understood that the sync signal generator 92 mayinclude two separate output channels one of which is connected to thepulsing network and the other of which is connected to the conductorpair 250 for transmission of the sync signal to the surface equipment.By thus providing separate and distinct output circuit paths from thesync signal generator 92 to the pulsing circuit 58 and to the conductorpair 250 a relatively sharp sync pulse can be transmitted over theconductor pair 250 without the influence of after pulse ringing or deadtime effects that may follow activation of the pulsing circuit 58.

At the surface end of the transmission system comprising cable 220, theshield of each conductor pair is left in a floating or non-connectedcondition, i.e., there is no connection provided between the shieldassociated with the respective twisted pairs and the conductors of therespective pairs or with ground. In the downhole logging instrument 22of the apparatus shown in FIG. 5, it is to be understood that one of thetwo conductors of each of the four twisted pairs is connected (notillustrated) to its respective copper braided shield. In the downholelogging instrument 22 of FIG. 5 neither of the individual conductors ofeach of the first and second twisted pairs 244 and 246 are connected tocommon ground. However, one of the conductors of the twisted pair 250and one of the conductors of the twisted pairs 252 are connected tocommon ground as illustrated in FIG. 5. Although not shown in thedrawings, the conductive sheath or shield of the pair 252 is connectedto the grounded one of the pair 252. Likewise the conductive sheath ofthe twisted pair 250 is connected to the grounded conductor of the pair250.

The individual conductors 301 and 302 are not specifically illustratedin FIGS. 57 since they are not necessary to the operation of thedisclosed apparatus. Individual conductors 301 and 302 of the cable 220serve the purpose of spacers in the cable and are available for use inconducting other logging functions such as electric logging functionsnot illustrated in the figures of the drawings and which are notdirectly concerned with the disclosed invention.

It is to be understood that the elements of FIGS. 5, 6 and 7 notspecifically described correspond to the elements bearing correspondingreference numbers in FIGS. 1-4.

Obviously many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

We claim:

1. Au acoustical velocity well logging system comprising an elongatedtool adapted to be passed through the bore of a well, an acoustic pulsegenerating circuit including a first electroacoustic-al transducersupported by said tool and adapted to produce an acoustic pulse fortravel through a subsurface formation opposite said tool between twospaced apart points on said tool and means for actuating said transducerincluding trigger pulse producing means, a first transformer having anoutput operatively coupled to said transducer, a pulse forming networkoperatively coupled to an input of said first transformer, means forelectrically charging said network, means for discharging the energy insaid pulse-forming network through said first transformer to said firsttransducer comprising a silicon controlled rectifier having ananode-cathode output circuit and an input circuit including a controlelement, said controlled rectifier input circuit being operativelycoupled to said trigger pulse-producing means, said controlled rectifieroutput circuit being operatively coupled to said pulse forming networkand to said transformer to discharge the energy in said pulse formingnetwork into said transformer upon the arrival thereat of a pulse fromsaid trigger pulse producing means, and means for measuring the time oftravel of said acoustic pulse between said two points, said measuringmeans including a second electroacoustical transducer supported by saidtool at a fixed distance from said first transducer and responsive tosaid acoustic pulse and a coaxial cable operatively coupled to saidsecond transducer to transmit the output thereof to the earths surfaceand apparatus at the earths surface operatively coupled to said coaxialcable for providing a signal indication proportional to the time oftravel of said acoustic pulse between said two points as a measure ofthe velocity of said acoustic pulse travelling through the subsurfaceformation opposite said tool.

2. An acoustical velocity well logging system set forth in claim 1wherein said measuring means further includes a second transformercoupling the output from said second transducer to said cable and saidtool includes a first housing disposed at one end thereof to house saidfirst transformer, said pulse forming network and said siliconcontrolled rectifier and a second housing disposed at the opposite endthereof to house said second transformer, said first electroacousti-caltransducer being disposed between said second housing and said one endof said tool.

3. An acoustical velocity well logging system comprising an elongatedtool adapted to be passed through the bore of a well, means fortransmitting an acoustic pulse through earth formations including anacoustical transmitting transducer, an acoustic pulse generating circuitincluding said acoustical transmitting transducer, a first transformerhaving a primary winding and a secondary winding coupled to saidtransducer, a pulse forming network and a silicon controlled rectifierdisposed within said tool at the upper end thereof, means forelectrically charging said network, said silicon controlled rectifierhaving an output circuit and an input circuit including a controlelement, means for periodically discharging said pulse-forming networkthrough the primary winding of said first transformer including atrigger pulse producing means disposed at the earths surface and coupledto the control element of said silicon controlled rectifier, the outputof said silicon controlled rectifier being operatively connected to saidpulse forming network and to said primary winding so as to periodicallycouple said pulse forming network to the primary winding of saidtransformer, means for detecting an acoustic pulse transmitted throughearth formations from said acoustic transmitting transducer comprisingfirst and second acoustic pulse receiving transducers longitudinallyspaced apart from each other and from said transmitting transducer,first and second coaxial cables, means including a second transformerfor coupling said first receiving transducer to one end of said firstcoaxial cable, means including a third transformer for coupling saidsecond receiving transducer to one end of said second coaxial cable,said first and second receiving transducers and said second and thirdtransformers being disposed in said tool at the lower end thereof, andtime measuring means coupled to the other end of said first and secondcoaxial cables for providing an indication of the time interval betweenthe detection of an acoustic pulse by said first and second acousticpulse receiving transducers,

4. An acoustical velocity well logging system comprising an elongatedhousing adapted to be passed through the bore of a well, means includingan acoustical transmitting transducer for transmitting an acoustic pulsethrough earth formations, an acoustic pulse generating circuit includingsaid acoustical transmitting transducer, a first transformer having aprimary winding and a secondary winding coupled to said transducer,energy storing means and a silicon controlled rectifier disposed withinsaid housing at the upper end thereof, said controlled rectifier havingan output circuit and an input circuit including a control element,trigger pulse producing means disposed at the earths surface, means forapplying the output from said trigger pulse producing means to thecontrol element of said silicon controlled rectifier and means forsupplying energy to said energy storing means, means including theoutput circuit of said silicon controlled rectifier for periodicallydischarging the energy in said storing means through the primary windingof said first transformer, means for detecting an acoustic pulsetransmitted through earth formations from said acoustical transmittingtransducer comprising first and second acoustic pulse receivingtransducers longitudinally spaced apart from each other and from saidtransmitting transducer, first and second coaxial cables, meansincluding a second transformer for coupling said first receivingtransducer to second receiving transducers and said second and thirdtransformer for coupling said second receiving transducer to one end ofsaid second coaxial cable, said first and second receiving transducersand said second and third transformers being disposed in said housing atthe lower end thereof, and time measuring means coupled to the other endof said first and second coaxial cables for providing an indication ofthe time interval between the detection of an acoustic pulse by saidfirst and second acoustic pulse receiving transducers.

5. An acoustical velocity well logging system comprising an elongatedtool adapted to be passed through the bore of a well, an acoustic pulsegenerating circuit including a first electroacoustical transducer and asemiconductor device of the solid-state thyratron type for producing anacoustic pulse at periodic intervals, a transformer having a primary anda secondary winding, the secondary winding of said transformer beingcoupled to said first electroacoustical transducer, said semi-conductordevice having an output circuit and an input circuit, an electricalenergy storing network, means for charging said energy storing network,means including the output circuit of said semi-conductor device fordischarging said network through the primary winding of saidtransformer, a second electroacoustical transducer, said first andsecond electroacoustical transducers being at a fixed spaced apartdistance from each other and supported by said tool, a coaxial cable,means for applying the output from said second transducer to one end ofsaid coaxial cable and means coupled to said acoustic pulse generatingcircuit and to the other end of said coaxial cable for measuring thetime of travel of one of the acoustic pulses between said first andsecond transducers.

6. An acoustical velocity well logging system comprising an elongatedtool adapted to be passed through the bore of a well, an acoustic pulsegenerating circuit including a first electroacoustical transducersupported by said tool and adapted to produce an acoustical pulse fortravel through a subsurface formation opposite said tool between twospaced apart points on said tool and means for actuating said transducerincluding trigger pulse producing means, a first transformer having anoutput operatively coupled to said transducer, a pulse forming networkoperatively coupled to an input of said first transformer, means forelectrically charging said network, means for discharging the energy insaid pulse-forming network through said first transformer to said firsttransducer comprising a silicon controlled rectifier having ananodecathode output circuit and an input circuit including a controlelement, said controlled rectifier input circuit being operativelycoupled to said trigger pulse-producing means, said controlled rectifieroutput circuit being operatively coupled to said pulse forming networkand to said transformer to discharge the energy in said pulse formingnetwork into said transformer upon the arrival thereat of a pulse fromsaid trigger pulse producing means, and means for measuring the time oftravel of said acoustic pulse between said two points, said measuringmeans including a second electroacoustical transducer supported by saidtool at a fixed distance from said first transducer and responsive tosaid acoustic pulse and a signal transmission system operatively coupledto said second transducer to transmit the output thereof to the earthssurface and apparatus at the earths surface operatively coupled to saidsignal transmission system for providing a signal indicationproportional to the time of travel of said acoustic pulse between saidtwo points as a measure of the velocity of said acoustic pulsetravelling through the subsurface formation opposite said tool, saidapparatus further including a second transformer directly coupling saidsecond transducer to said signal transmission system.

7. An acoustical velocity well logging system set forth in claim 6wherein said measuring means further includes a third transducer and athird transformer directly coupling the output from said second thirdtransducer to said signal transmission system and said tool includes afirst housing disposed at one end thereof to house said firsttransformer, said pulse forming network and said silicon controlledrectifier and a second housing disposed at the opposite end thereof tohouse said second transformer, said first electroacoustical transducerbeing disposed between said second housing and said one end of saidtool.

8. An acoustical velocity well logging system comprising an elongatedtool adapted to be passed through the bore of a well, means fortransmitting an acoustic pulse through earth formations including anacoustical transmitting transducer, an acoustic pulse generating circuitincluding said acoustical transmitting transducer, a first transformerhaving a primary winding and a secondary winding coupled to saidtransducer, a pulse forming network and a silicon controlled rectifierdisposed within said tool at the upper end thereof, means forelectrically charging said network, said siiicon controlled rectifierhaving an output circuit and an input circuit including a controlelement, means for periodically discharging said pulse-forming networkthrough the primary winding of said first transformer including atrigger pulse producing means coupled to the control element of saidsilicon controlled rectifier, the output of said silicon controlledrectifier being operatively connected to said pulse forming network andto said primary winding so as to periodically couple said pulse formingnetwork to the primary winding of said transformer, means for detectingan acoustic pulse transmitted through earth formations from saidacoustic transmitting transducer comprising first and second acousticpulse receiving transducers longitudinally spaced apart from each otherand from said transmitting transducer, a signal transmission systemcomprising first and second transmission circuits, means including asecond transformer for directly coupling said first receiving transducerto one end of said first transmission circuit, means including a thirdtransformer for directly coupling said second receiving transducer toone end of said second transmission circuit, said first and secondreceiving transducers and said second and third transformers beingdisposed in said tool at the lower end thereof, and time measuring meanscoupled to the other end of said first and second transmission circuitsfor providing an indication of the time interval between the detectionof an acoustic pulse by said first and second acoustic pulse receivingtransducers.

9. An acoustical velocity well logging system comprising an elongatedtool adapted to be passed through the bore of a well, an acoustic pulsegenerating circuit including a first electroacoustical transducer and asemiconductor device of the solid-state thyratron type for producing anacoustic pulse at periodic intervals, a first transformer having aprimary and a secondary winding, the secondary winding of saidtransformer being coupled to said first electroacoustical transducer,said semi-conductor device having an output circuit and an inputcircuit, an electrical energy storing network, means for charging saidenergy storing network, means including the output circuit of saidsemi-conductor device for discharging said network through the primarywinding of said transformer, second and third electroacoustical transducers, said second and third electroacoustical transducers being spacedfrom said first transducer and being at a fixed spaced apart distancefrom each other and supported by said tool, a signal transmissionsystem, means including second and third transformer for applying therespective outputs from said second and third transducers directly toone end of said signal transmission system and means coupled to theother end of said signal transmission system for measuring the time oftravel of one of the acoustic pulses between said second and thirdtransducers.

10. An acoustical velocity Well logging system comprising an elongatedtool adapted to be passed through the bore of a well, an acoustic pulsegenerating circuit inluding a first electroacoustical transducer and adevice for producing an acoustic pulse at periodic intervals, a firsttransformer having a primary and a secondary winding, the secondaryWinding of said transformer being coupled to said firstelectroacoustical transducer, said device having an output circuit andan input circuit, an electrical energy storing network, means forcharging said energy storing network, means including the output circuitof said device for discharging said network through the primary Windingof said first transformer, a second and a third electroacousticaltransducer, said sec ond and third electroacoustical transducers beingat a fixed spaced apart distance from each other and from said firsttransducer and being supported by said tool, a signal transmissionsystem, means including the second and third transformers, for applyingthe respective out puts directly from said second and third transducersto one end of said signal transmission system and means coupled to saidacoustic pulse generating circuit and to the other end of said signaltransmission system for measuring the time of travel of one of theacoustic pulses between said second and third transducers.

11. An acoustical velocity well logging system comprising an elongatedhousing adapted to be passed through the bore of a well, means includingan acoustical transmitting transducer for transmitting an acoustic pulsethrough earth formations, an acoustic pulse generating circuit includingsaid acoustical transmitting transducer, a first transformer having aprimary winding and a secondary winding coupled to said transducer,energy storing means and a silicon controlled rectifier disposed withinsaid housing at the upper end thereof, said controlled rectifier havingan output circuit and an input circuit including a control element,trigger pulse producing means, for applying the output from said triggerpulse producing means to the control element of said silicon controliedrectifier and means for supplying energy to said energy storing means,means including the output circuit of said silicon controlled rectifierfor periodically discharging the energy in said storing means throughthe primary Winding of said first transformer, means for detecting anacoustic pulse transmitted through earth formations from said acousticaltransmitting transducers comprising first and second acoustic pulsereceiving transducers longitudinally spaced apart from each other andfrom said transmitting transducer, means defining first and secondsignal transmission paths, means including a second transformer forcoupling said first receiving transducer to one end of the meansdefining said first signal path, means including a third transformer forcoupling said second receiving transducer to one end of the meansdefining said second signal path, said first and second receivingtransducers and said second and third transformers being disposed insaid housing at the lower end thereof, and time measuring means coupledto the other end of the means defining said first and second signalpaths for providing an indication of the time interval between thedetection of an acoustic pulse by said first and second acoustic pulsereceiving transducers.

12. An acoustical velocity well logging system comprising an elongatedtool adapted to be passed through the bore of a well, an acoustic pulsegenerating circuit including a first electroacoustical transducersupported by said tool and adapted to produce an acoustic pulse fortravel through a subsurface formation opposite said tool between twospaced apart points on said tool and means for actuating said transducerincluding trigger pulse producing means, a first transformer having anoutput operatively coupled to said transducer, a pulse forming networkoperatively coupled to an input of said first transformer, means forelectrically charging said network, means for discharging the energy insaid pulse-forming network through said first transformer to said firsttransducer comprising a silicon controlled rectifier having ananode-cathode output circuit and an input circuit including a controlelement, said controlled rectifier input circuit being operativelycoupled to said trigger pulse-producing means, said controlled rectifieroutput circuit being operatively coupled to said pulse forming networkand to said transformer to discharge the energy in said pulse formingnetwork into said transformer upon the arrival thereat of a pulse fromsaid trigger pulse producing means, and means for measuring the time oftravel of said acoustic pulse between said two points, said measuringmeans including a second electroacoustical transducer supported by saidtool at a fixed distance from said first transducer and responsive tosaid acoustic pulse and a coaxial cable operatively coupled to saidsecond transducer to transmit the output thereof to the earths surfaceand apparatus at the earths surface operatively coupled to said coaxialcable for providing a signal indication proportional to the time oftravel of said. acoustic pulse between said two points as a measure ofthe velocity of said acoustic pulse travelling through the subsurfaceformation opposite said tool, and wherein said tranrformer is a step-uptransformer and said acoustic pulse generating circuit further includesrectifying means connected across the ouput of said transformer.

13. An acoustical velocity well logging system comprising an elongatedtool adapted to be passed through the bore of a well, an acoustic pulsegenerating circuit including a first electroacoustical transducersupported by said tool and adapted to produce an acoustic pulse fortravel through a subsurface formation opposite said tool between twospaced apart points on said tool and means for actuating said transducerincluding trigger pulse producing means, a first transformer having anoutput operatively coupled to said transducer, a pulse forming networkoperatively coupled to an input of said first transformer, means forelectrically charging said network, means for discharging the energy insaid pulseforming network through said first transformer to said firsttransducer comprising a silicon controlled rectifier having ananode-cathode output circuit and an input circuit including a controlelement, said controlled rectifier input circuit being operativelycoupled to said trigger pulse-producing means, said controlled rectifieroutput circuit being operatively coupled to said pulse forming networkand to said transformer to discharge the energy in said pulse formingnetwork into said transformer upon the arrival thereat of a pulse fromsaid trigger pulse producing means, and means for measuring the time oftravel of said acoustic pulse between said two points, said measuringmeans including a second electroacoustical transducer supported by saidtool at a fixed distance from said first transducer and responsive tosaid acoustic pulse and a coaxial cable operatively coupled to saidsecond transducer to transmit the output thereof to the earths surfaceand apparatus at the earths surface operatively coupled to said coaxialcable for providing a signal indication proportional to the time oftravel of said acoustic pulse between said two points as a measure ofthe velocity of said acoustic pulse travelling through the subsurfaceformation opposite said tool, and wherein said acoustic pulse generatingcircuit further includes rectifying means con- 15 nected in parallelwith the anode-cathode circuit of said silicon controlled rectifier.

14. An acoustical velocity well logging system comprising an elongatedtool adapted to be passed through the bore of a wall, an acoustic pulsegenerating circuit including a first electroacoustical transducersupported by said tool and adapted to produce an acoustic pulse fortravel through a subsurface formation opposite said tool between twospaced apart points on said tool and means for actuating said transducerincluding trigger pulse producing means, a first transformer having anoutput operatively coupled to said transducer, a pulse forming networkoperatively coupled to an input of said first transformer, means forelectrically charging said network, means for discharging the energy insaid pulse-formingnetwork through said first transformer to said firsttransducer comprising a silicon controlled rectifier having ananode-cathode output circuit and an input circuit including a controlelement, said controlled rectifier input circuit being operativelycoupled to said trigger pulse-producing means, said controlled rectifieroutput circuit being operatively coupled to said pulse forming networkand to said transformer to discharge the energy in said pulse formingnetwork into said transformer upon the arrival thereat of a pulse fromsaid trigger pulse producing means, and means for measuring the time oftravel of said acoustic pulse between said two points, said measuringmeans including a second electroacoustical transducer supported by saidtool at a fixed distance from said first transducer and responsive tosaid acoustic pulse and a coaxial cable operatively coupled to saidsecond transducer to transmit the output thereof to the earths surfaceand apparatus at the earths surface operatively coupled to said coaxialcable for providing a signal indication proportional to the time oftravel of said acoustic pulse between said two points as a measure ofthe velocity of said acoustic pulse travelling through the subsurfaceformation opposite said tool, and wherein the trigger pulse producingmeans of said acoustic pulse generator includes a first diode connectedto the control element of said silicon controlled rectifier so as toreadily pass the trigger pulse therethrough to said control element anda second diode connected between the control element of said siliconcontrolled rectifier and a point of ground potential so as to provide ahigh impedance path for the trigger pulse.

15. An acoustical velocity well logging system comprising an elongatedtool adapted to be passed through the bore of a well, an acoustic pulsegenerating circuit including a first electroacoustical transducersupported by said tool and adapted to produce an acoustical pulse fortravel through a subsurface formation opposite said tool between twospaced apart points on said tool and means for actuating said transducerincluding trigger pulse producing means, a first transformer having anoutput operatively coupled to said transducer, a pulse forming networkoperatively coupled to an input of said first transformer, means forelectrically charging said network, means for discharging the energy insaid pulse-forming network through said first transformer to said firsttransducer comprising a silicon controlled rectifier having ananode-cathode output circuit and an input circuit including a controlelement, said controlled rectifier input circuit being operativelycoupled to said trigger pulse-producing means, said controlled rectifieroutput circuit being operatively coupled to said pulse forming networkand to said transformer to discharge the energy in said pulse formingnetwork into said transformer upon the arrival thereat of a pulse fromsaid trigger pulse producing means, and means for measuring the time oftravel of said acoustic pulse between said two points, said measuringmeans including a second electroacoustical transducer supported by saidtool at a fixed distance from said first transducer and responsive tosaid acoustic pulse and a signal transmission system operatively coupledto said second transducer to transmit the output thereof to the earthssurface and apparatus at the earths surface operatively coupled to saidsignal transmission system for providing a signal indicationproportional to the time of travel of said acoustic pulse between saidtwo points as a measure of the velocity of said acoustic pulse travelingthrough the subsurface formation opposite said tool, and wherein saidtransformer is a step-up transformer and said acoustic pulse generatingcircuit further includes rectifying means connected across the output ofsaid transformer.

16. An acoustical velocity well logging system comprising an elongatedtool adapted to be passed through the bore of a well, an acoustic pulsegenerating circuit including a first electroacoustical transducersupported by said tool and adapted to produce an acoustical pulse fortravel through'a subsurface formation opposite said tool between twospaced apart points on said tool and means for actuating said tranducerincluding trigger pulse producing means, a first transformer having anoutput operatively coupled to said transducer, a pulse forming networkoperatively coupled to an input of said first transformer, means forelectrically charging said network, mans for discharging the energy insaid pulse-forming network through said first transformer to said firsttransducer comprising a silicon controlled rectifier having ananode-cathode output circuit and an input circuit including a controlelement, said controlled rectifier input circuit being operativelycoupled to said trigger pulse-producing means, said controlled rectifieroutput circuit being operatively coupled to said pulse forming networkand to said transformer to discharge the energy in said pulse formingnetwork into said transformer upon the arrival thereat of a pulse fromsaid trigger pulse producing means, and means for measuring the time oftravel of said acoustic pulse between said two points, said measuringmeans including a second electroacoustical transducer supported by saidtool at a fixed distance from said first transducer and responsive tosaid acoustic pulse and a signal transmission system operatively coupledto said second transducer to transmit the output thereof to the earthssurface and apparatus at the earths surface operatively coupled to saidsignal transmission system for providing a signal indicationproportional to the time of travel of said acoustic pulse between saidtwo points as a measure of the velocity of said acoustic pulsetravelling through the subsurface formation opposite said tool, andwherein said acoustic pulse generating circuit further includesrectifying means connected in parallel with the anode-cathode circuit ofsaid silicon controlled rectifier.

17. An acoustical velocity well logging system comprising an elongatedtool adapted to be passed through the bore of a well, an acoustic pulsegenerating circuit including a first electroacoustical transducersupported by said tool and adapted to produce an acoustical pulse fortravel through a subsurface formation opposite said tool between twospaced apart points on said tool and means for actuating said transducerincluding trigger pulse producing means, a first transformer having anoutput operatively coupled to said transducer, a pulse forming networkoperatively coupled to an input of said first transformer, means forelectrically charging said network, means for discharging the energy insaid pulse-forming network through Said first transformer to said firsttransducer comprising a silicon controlled rectifier having ananode-cathode output circuit and an input circuit including a controlelement, said controlled rectifier input circuit being operativelycoupled to said trigger pulse-producing means, said controlled rectifieroutput circuit being operatively coupled to said pulse forming networkand to said transformer to discharge the energy in said pulse formingnetwork into said transformer upon the arrival thereat of a pulse fromsaid trigger pulse producing means, and means for measuring the time oftravel of said acoustic pulse between said two points, said measuringmeans including a second electroacoustical transducer supported by saidtool at a fixed distance from said first transducer and responsive tosaid 17 acoustic pulse and a signal transmission system operativelycoupled to said second transducer to transmit the output thereof to theearths surface and apparatus at the earths surface operatively coupledto said signal transmission system for providing a signal indicationproportional to the time of travel of said acoustic pulse between saidtwo points as a measure of the velocity of said acoustic pulsetravelling through the subsurface formation opposite said tool, andwherein the trigger pulse producing means of said acoustic pulsegenerator includes a first diode connected to the control element ofsaid silicon controlled rectifier so as to readily pass the triggerpulse therethrough to said control element and a second diode connectedbefier and a point of ground potential so as to provide a high impedancepath for the trigger pulse.

References Cited BENJAMIN A. BORCHELT, Primary Examiner. SAMUELFEINBERG, Examiner.

tween the control element of said silicon controlled recti- 15 R. M.SKOLNIK, Asuistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,368,196 February 6 1968 Roy P. Mazzagatti et al.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 4, line 35, "be elapsed" should read the elapsed line 48, "Apr.15, 1960" should read Apr. 5, 1960 Column 7, line 32, "didoes" shouldread diodes line 39, "didoes" should read diodes Column 8, line 49,"fiberglass" should read fiberglas Column 11, line 16, "second receivingtransducers and second and third" should read one end of said firstcoaxial cable, means including a third Column 14, line 34, "tranrformer"should read transformer Column 16, line 21, "mans" should read meansSigned and sealed this 19th day of August 1969. (SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, 11'.

Commissioner of Patents Attesting Officer

